Electrical power for an integrated circuit (IC) may typically be supplied by one or more direct current (DC) sources. More particularly, today's large-scale high-speed digital processors typically require low voltages (e.g., Vdd), large currents (e.g., Idd), and a high through rate DC-DC converter for the power supply. Multi-phase DC-DC converter circuits are widely used for such applications. For high through rates and high efficiency, DC-DC converters typically need a driver and switching circuit such as a driver and metal-oxide semiconductor field-effect transistors built- in device called a “driver MOS” to help eliminate stray induction between the driver and the switching MOSFETs.
Usually, a current driving capacity of a single driver MOS may not be sufficient for use with a digital processor, so a multi-phase driver MOS circuit configuration is used to provide multi channel parallel operation. A voltage feedback from an output to each PWM generator produces stable DC output. Each driver MOS may also have an output current sensing and negative feedback loop. The current sensing feedback works to get all of driver MOS devices to share current equally. For such current sensing, many systems have been proposed.
FIG. 1 illustrates a current sensing technology 100 that uses a low side MOSFET RDSON (“RDSON” meaning the on-state resistance that exists between the drain and source) as a sensing resistor. In the FIG. 1, the current flow through a low side switching MOSFET is monitored via the low side MOSFET RDSON. Such a system 100 may be useful for high efficiency operation and at low cost. However, such a system 100 must be carefully designed in order to account for RDSON deviation and temperature dependency. FIG. 2 illustrates a multi-phase DC-DC converter (in this example a two phase converter) using the current sensing methodology 100 shown in FIG. 1.
FIG. 3 illustrates another current sensing technology 300 using common serial resistors between a high side MOSFET and VIN power rail. In the system 300 shown in FIG. 3, the common drain current is monitored using a resistor. This system may be effective for achieving good current matching for each driver MOS. However, drain line impedance in this system is extremely sensitive making efficiency very difficult under high current operation.
FIG. 4 illustrates an additional current sensing technology 400 that uses the parasitic resistance of an inductor. In the FIG. 4, the current through to an inductor is monitored using the parasitic resistance of the inductor. This system 400 may have a good efficiency at a relatively low cost. However, careful design is required for such systems 400 in order to account for filter frequency and temperature dependency.